Magnetic properties of dense holographic QCD

TL;DR

This paper explores the magnetic properties of dense holographic QCD using the Sakai-Sugimoto model, revealing phase transitions, pion gradients, and paramagnetic behavior under strong magnetic fields.

Contribution

It provides a detailed analysis of magnetic effects on dense holographic QCD, including phase transitions and induced currents, with new insights into baryonic matter behavior.

Findings

Gradient of pion carries baryon charge in confined phase

Second order phase transition to mixed phase at critical chemical potential

Magnetization is paramagnetic with nonlinear behavior at high magnetic fields

Abstract

We investigate the Sakai-Sugimoto model at nonzero baryon chemical potential in a background magnetic field both in the confined phase and in the deconfined phase with restored chiral symmetry. In this case the 8-brane Chern-Simons term becomes important. In the confined phase it generates a gradient of the pseudo-scalar "pion", which carries a non-vanishing baryon charge. Above a critical value of the chemical potential there is a second order phase transition to a mixed phase which includes also ordinary baryonic matter. However, at fixed baryon charge density the matter is purely "pion"-gradient above a critical magnetic field. In the deconfined chiral-symmetric phase at nonzero chemical potential the magnetic field induces an axial current. We also compute the magnetization of the baryonic matter and find that it is paramagnetic in all three phases but with nonlinear behavior at large magnetic field.